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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 5 |
| 3 | 20 |
| 4 | 90 |
| 5 | 499 |
| 6 | 3395 |
| 7 | 27474 |
| 8 | 256984 |
| 9 | 2720169 |
| 10 | 32080501 |
| 11 | 416574212 |
| 12 | 5900292266 |
| 13 | 90461885331 |
| 14 | 1491788697451 |
| 15 | 26318520300986 |
| 16 | 494449968500832 |
| 17 | 9852544385880961 |
| 18 | 207497251731808341 |
| 19 | 4604297325494524516 |
| 20 | 107348917822006139114 |
| 21 | 2623224641748615607715 |
| 22 | 67035139167875735937219 |
[0,1,5,20,90,499,3395,27474,256984,2720169, 32080501,416574212,5900292266,90461885331, 1491788697451,26318520300986,494449968500832, 9852544385880961,207497251731808341, 4604297325494524516,107348917822006139114, 2623224641748615607715,67035139167875735937219] |